1. Measuring sea ice thickness using satellite radar altimetry
Rosemary Willatt Seymour Laxon, Katharine Giles
Centre for Polar Observation and Modelling (CPOM)
UCL

2. Presentation Contents
What is sea ice?
Satellite radar altimetry
success
unresolved issues
My PhD
Results
Future work

3. What is sea ice?
Telegraph.co.uk (2007)

4. Why is sea ice important?
Sea ice forms when sea water freezes.
Reduces heat/moisture exchange between ocean and atmosphere
It affects the Earth’s albedo.
Large volume of stored fresh water.

5. Sea ice in the thermohaline circulation
Hugo Ahlenius, UNEP/GRID-Arendal (2007)

6. Satellite Radar Altimetry
Satellite-mounted radar
Ice thickness calculation:
1) Signal transmitted downwards
2) Signal reflected back off water and ice
3) Measure height of ice above water
4) Calculate ice thickness using assumption of hydrostatic equilibrium

7. Radar Penetration Radar altimeter: measure sea ice freeboard
Penetration: assume reflection is from snow/ice interface
Ku-band (13.5 GHz) radar penetration through Antarctic and Arctic snow

8. Satellite radar altimetry – success in Arctic (winter)
Laxon et al. (2003)

9. Satellite radar altimetry – issue of penetration
Penetration of radar through snow cover?
Proven in laboratory, not in the field
Arctic results indicate penetration to snow/ice interface
Antarctica
variable temperature and wind conditions
complex snow pack

10. Antarctic – can satellite radar altimetry be used?
Giles et al., 2008
Used satellite radar altimetry data to derive ice elevations
Compared with the ASPeCt dataset
Pattern of ice elevation was in good agreement
Altimetry-derived ice elevations were too high
one suggestion by authors is that radar return originates from between air/snow and snow/ice interfaces

11. My PhD Issue of penetration of radar into snow cover
Antarctic study: fieldwork in Antarctica
Arctic study: airborne radar data
CryoSat (ESA) - launch in December 2009

12. Antarctic Fieldwork Six week trip to Antarctica
Investigating radar penetration into snow cover
Gathering data in GHz band using sledge-based radar

18. Experimental setup

19. Analysis
radar measured
air/snow interface
snow/ice interface

20. Dominant scattering surfaces in radar return echoes
Analysis: air/snow interface, layer in the snow pack or snow/ice interface
dominant scattering surface in the radar return echoes
snow/ice interface 30%
air/snow interface 43% within snow pack 23%
ambiguous 3%
Mean depth of dominant scattering surface of radar ~50% mean measured snow depth
Willatt et al., in press

21. Current project Future work Radar penetration into Arctic snow cover
Airborne data from ASIRAS
Data obtained in May – snow conditions typical of those in Arctic winter?
Future work
Simulation of ASIRAS echoes – also for SIRAL (CryoSat)
Use of altimetry data (other bands, radar and laser) to measure Antarctic sea ice thickness

22. Thank you!
Any questions?